Remove default docker pipeline stage - this is undocumented and unexp…

…ected behaviour (#3404)

Signed-off-by: Danny Kopping <danny.kopping@grafana.com>

pkg/promtail/scrapeconfig/scrapeconfig.go

@@ -240,11 +240,7 @@ type PushTargetConfig struct {
 
 // DefaultScrapeConfig is the default Config.
 var DefaultScrapeConfig = Config{
-	PipelineStages: []interface{}{
-		map[interface{}]interface{}{
-			stages.StageTypeDocker: nil,
-		},
-	},
+	PipelineStages: stages.PipelineStages{},
 }
 
 // HasServiceDiscoveryConfig checks to see if the service discovery used for

pkg/promtail/scrapeconfig/scrapeconfig_test.go

@@ -80,6 +80,18 @@ relabel_configs:
   target_label: __path__
 `
 
+var noPipelineStagesYaml = `
+job_name: kubernetes-pods-name
+static_configs:
+- targets:
+    - localhost
+  labels:
+    job: varlogs
+    __path__: /var/log/*log
+kubernetes_sd_configs:
+- role: pod
+`
+
 func TestLoadSmallConfig(t *testing.T) {
 	var config Config
 	err := yaml.Unmarshal([]byte(smallYaml), &config)
@@ -109,6 +121,15 @@ func TestLoadSmallConfig(t *testing.T) {
 	require.Equal(t, expected, config)
 }
 
+// bugfix: https://github.com/grafana/loki/issues/3403
+func TestEmptyPipelineStagesConfig(t *testing.T) {
+	var config Config
+	err := yaml.Unmarshal([]byte(noPipelineStagesYaml), &config)
+	require.Nil(t, err)
+
+	require.Zero(t, len(config.PipelineStages))
+}
+
 func TestLoadConfig(t *testing.T) {
 	var config Config
 	err := yaml.Unmarshal([]byte(testYaml), &config)